Barack Obama, is to send 1,200 National Guard troops to the country's border with Mexico to bolster security, an administration official said yesterday.

The move pre-empts Republican plans to try to force a vote on such a deployment and comes as Obama seeks cross-party support for a sweeping overhaul of US immigration laws.

The US president has also been trying to galvanise opposition to a tough new immigration law in Arizona that has strained the country's relations with Mexico.

The new law required police officers in the state to determine the status of people if there was "reasonable suspicion" that they were illegal immigrants, and to arrest those unable to provide documents proving they were in the country legally.

The legislation, the toughest in the US, was aimed at driving 460,000 illegal immigrants out of the desert state, which straddles one of the principal corridors for human and drug smugglers heading up from Mexico. It was criticised by Obama but put the spotlight on illegal immigration.

US officials are concerned that drug-related violence will cross the border from Mexico, where some 23,000 people have been killed since Felipe Calderon was elected president in late 2006 as drug gangs have fought turf wars and battled federal agents.

Obama will also request $500m (£347m) for border protection and law enforcement activities, the administration official said. The National Guard troops will work on intelligence, surveillance and reconnaissance support, analysis and training, and support efforts blocking drug trafficking. The troops will temporarily supplement border patrol agents until customs and border patrol can recruit and train additional officers and agents to serve on the border, the official said.

The plans were disclosed by the official after the president met Republican senators who pressed him on immigration issues including their desire for guard troops to be sent to the border.

John McCain, defeated by Obama in the 2008 presidential race, and fellow Arizona senator Jon Kyl were among those arguing for a deployment and Republicans were planning to try to attach it as an amendment to a pending war spending bill.

McCain gave a lukewarm response to news that additional guard troops were to be dispatched. Speaking on the Senate floor, he said there was a need for 6,000 troops in total, describing the situation on the border as "greatly deteriorated".

"I appreciate the additional 1,200 being sent … as well as an additional $500m but it's simply not enough," he said.

Homeland Security and Pentagon officials have been debating possible National Guard deployment for the best part of a year. Pentagon officials were worried that the US would be perceived as militarising the border and did not want guard troops to perform law enforcement duties. Members of the National Guard are civilians who train once a week and one month during the summer in units that can be mobilised for military duty or emergency relief. There are currently 344 National Guard troops working along the border. The administration planned to announce the deployment officially late last night.